Reflections on O2 as a Biosignature in Exoplanetary Atmospheres.
TLDR
Environmental factors for abiotic O2 have been identified and will improve the ability to choose optimal targets and measurements to guard against false positives, and thorough evaluation of potential biosignatures works to increase confidence in life detection.Abstract:
Oxygenic photosynthesis is Earth's dominant metabolism, having evolved to harvest the largest expected energy source at the surface of most terrestrial habitable zone planets. Using CO2 and H2O—molecules that are expected to be abundant and widespread on habitable terrestrial planets—oxygenic photosynthesis is plausible as a significant planetary process with a global impact. Photosynthetic O2 has long been considered particularly robust as a sign of life on a habitable exoplanet, due to the lack of known “false positives”—geological or photochemical processes that could also produce large quantities of stable O2. O2 has other advantages as a biosignature, including its high abundance and uniform distribution throughout the atmospheric column and its distinct, strong absorption in the visible and near-infrared. However, recent modeling work has shown that false positives for abundant oxygen or ozone could be produced by abiotic mechanisms, including photochemistry and atmospheric escape. Environm...read more
Citations
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Habitability and Biosignatures of Hycean Worlds
TL;DR: In this article, the authors investigate a new class of habitable exoplanets composed of water-rich interiors with massive oceans underlying H2-rich atmospheres, referred to here as Hycean worlds.
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Exoplanet Terra Incognita
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Astrobiology and Development of Human Civilization
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Observing Isotopologue Bands in Terrestrial Exoplanet Atmospheres with the James Webb Space Telescope---Implications for Identifying Past Atmospheric and Ocean Loss.
TL;DR: In this article, post-ocean-loss O2-and CO2-dominated atmospheres, containing a range of trace gas abundances, were used to infer the history of ocean loss and atmospheric escape for terrestrial planets around M dwarfs.
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Molecular Regulation and Evolution of Redox Homeostasis in Photosynthetic Machinery
Adeel Riaz,Fenglin Deng,Guang Chen,Qingfeng Zheng,Bisma Riaz,Michelle Mak,Fanrong Zeng,Zhong-Hua Chen +7 more
TL;DR: A comprehensive comparative bioinformatic analysis of redox regulation in evolutionary distinct photosynthetic cells is presented, highlighting the importance of plant responses to stress cues and genetic manipulation of disturbed redox status for balanced and enhanced photosynthesis efficiency and plant productivity.
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